A collector system of the type with which the present invention is concerned is referred to as a Fresnel reflector system and, depending upon its configuration, may be considered as an analogue of a parabolic dish or a linear parabolic trough. When configured as an analogue of a parabolic trough, the collector system comprises receivers which are supported by vertical masts and which are orientated or arrayed to form a linearly extending target. The reflectors are positioned slightly above ground level and are arrayed over an area that is selected to provide reflection of the required amount of radiation toward the target receivers. The arrayed reflectors are orientated to reflect radiation toward one target, and the reflectors are pivotably mounted and coupled to provide for synchronised single-axis tracking.
The above described Fresnel reflector system permits the use of a large scale target and provides for low construction costs relative to those that would be incurred in equivalent size parabolic trough or dish collector systems. However, a problem that is inherent in the use of ground arrayed reflectors is that shading occurs as a consequence of radiation blockage. This takes two forms, one in which radiation that would fall incident on reflectors is blocked by adjacent reflectors and the other in which radiation that is reflected toward the target by some reflectors is blocked by adjacent reflectors. This problem might be avoided by spacing the reflectors in a manner to avoid shading, but this would have the two-fold effect of reducing land utilisation efficiency and expanding the distance between reflectors and associated target receivers. This in turn would have the effect of reducing circumsolar acceptance for a given geometrical concentration ratio and, in the case of a multi-target receiver system, of increasing pipe run lengths between the receiver systems.
The present invention seeks to avoid these problems, while preserving the benefit of the Fresnel reflector system, by providing for orientation of reflectors toward either one of two target receiver systems.